EDIT: This will improve desktop performance, but will make it so you are unable to connect to a multiplayer server!
If you're looking to improve your doom 3 performance, check out this information!
Use the following information at your own risk. I tried this, and it appears to work as noted below. My gameplay has improved quite a bit!
“I tried this and Im now runnig at 1280x1024 compared to 800x600 at the same settings.
"As all of you who allready have this game recognized the game is very slow even on new Computers.
I found out the reason for this and the solution to fix this problem.
As you already know after installation the game consits only of the doom3.exe and some .PK4 files. Those PK4 files includes the entire game (sounds, videos, textures etc.) in high compressed form.
Normally those files were decompresse during the game.
But this exactly is the problem. Even new CPUs are not able to decompress those files while running the game with good peformance and therfore the game runs very **** also on new computers. I don't know if the develpers of ID-Soft was just too stupid to think about this or if they have an agreement with some hardware manufacturing firms.
How to get around this problem:
It is very simple. Go to your Doom 3 installation directoy and get inside the folder "Base". There are some .PK4 files you have to open each of them with WinRAR 3.3 and extract their entire contents to the Base dir in you Doom 3 installation folder (replace all files if they are any duplicates). Now you have to delete all .PK4 files in the Base folder to prevent the game to use those compressed files agian.
Now the game starts and runs mutch faster!!!
Have fun playing Doom 3!!! "